Stratified volume holographic optical elements

Photoluminescence enhancement of GaN-based LEDs structure with nano-grayscale multiple quantum wells using electron beam lithography

ABSTRACTLiquid crystals (LCs) are widely used in nonlinear optics because of their sensitive responses to optical stimulation. Combined with other optoelectronic materials such as azo dyes, quantum dots (QDs), etc., LCs show very large optical nonlinearity which makes them suitable for applications in optical information processing, including holographic display and holographic storage. In this review, we present an overview of recent efforts on holographic display and storage based on liquid crystalline materials. Emphasis is placed on the dynamic holographic display which uses fast-response LCs doped with azo dye and QD. In this application, we discuss how to improve the response speed, resolution, and diffraction efficiency of liquid crystalline materials to realize high frame rate, large-size and high-brightness holographic displays. Some LC materials for holographic storage are also introduced, including polymer-dispersed liquid crystals, blue-phase liquid crystals, and azobenzene polymer liquid crystals, which have permanent response to light stimulation. The mechanisms of optical nonlinearities are discussed in detail, as a foundation for the physical process of LC-based holographic display and storage.

The multiple quantum well (MQW) structure is a good candidate to monolithically integrate lasers and waveguides for realizing photonic integrated circuits. For such an application, selective disordering techniques are required, because these can make it possible to define a waveguide section laterally by inducing local changes in absorption and refractive indices of a MQW structure, which is needed to fabricate waveguide devices including laser. There are several techniques to selectively disorder the I I I -V MQW structures. These are impurity induced disordering [1,2], ion implantation disordering [3, 4], and impurity-free disordering [5-12] followed by thermal treatment. Impurity induced disordering and ion implantation disordering can disorder MQW structure perfectly, but these techniques introduce many defects and high doping concentrations which may deteriorate the performances of waveguide devices because of losses from scatterings by defects and free carrier absorption in the waveguide. Impurity-free techniques employ dielectrics, such as SiO2 or SiN, a capped annealing technique, which employs rapid thermal annealing (RTA) [5-10] or sealed ampoule annealing with an As overpressure [11, 12]. Impurity-free techniques do not disorder MQW structure completely, but disorder it enough to fabricate waveguides and lasers [9-12]. For impurity-free disordering, there are various film growth techniques, such as chemical vapour deposition (CVD) [11], e-beam evaporation [6, 8, 9], sputtering [5], and plasma enhanced chemical vapour deposition (PECVD) [7, 10, 12], which can deposit SiN and/or Si te films on a MQW structure. The behaviour of disordering is affected by the film quality used in the impurity-free disordering technique. Therefore, if an optimum film growth condition can be found by varying process conditions, then selective disordering can be achieved with the same material without surface degradation which should be accompanied in the disordering process without an encapsulation. The characteristics of film deposited by the PECVD technique can be varied by varying process conditions, such as substrate temperature, ratio of reactant gas, and RF power [13]. As a first step to finding a process-dependent impurity-free disordering, we varied the RF power. We carried out impurity-free disordering using a PECVD SiN cap layer with RTA. We found that this technique could disorder the GaAs/A1GaAs MQW structure and the disordering was enhanced by using SiN film grown at high RF power. We used a GaAs/A1GaAs MQW laser structure which was grown by a metal organic chemical vapour deposition (MOCVD) technique on Si-doped n ÷ GaAs substrate. The structure has the following layers from the top of the substrate: 0.5/xm of n (1018 cm -3) GaAs buffer, 1/zm of n (1017 cm -3) A10.4~Ga0.s3As, 0.1/xm of undoped A10.24Ga0.76As, four 7 nm undoped GaAs quantum wells with 10 nm A10.24Ga0.76As barrier, 0.1/xm of undoped A10.24Ga0.76As, 1/zm of p (1017 cm -3) A10.47Ga0.53As, and 0.2/xm of p+ (10 ~8 cm -3) GaAs. In the substrate design, separate confinement design is chosen to enhance the optical confinement in the quantum wells. SiN films were deposited by a PECVD technique for cap layers. We used dilute silane (5% Sill4 in N:) and high purity NH 3 (99.999%) and N2 (99.9999%) as a reactant gas. During plasma deposition, the ratio of partial pressure (PNH3/Psi~,) was kept at 1, total pressure was kept as 120 Pa by adding N2 gas and the substrate temperature was 300 °C. SiN films were grown with various RF powers (0 W, 60 W and 90 W). The thicknesses and refractive indices, for each RF power condition, were determined by an ellipsometer (Gaertner, Ll17) and a surface profiler (Tencor, alpha step 200). Disordering of MQW samples was accomplished by RTA at 850 °C for 35 s in Ar atmosphere with a heating rate of 65 °C/s. Disordering of MQW

Due to its complex spatial distribution, the higher-order Hermite–Gaussian mode possesses significant application in fields such as precision measurement and optical communication. The spatial light modulator, with its capability to modulate the complex amplitude distribution of the incident light field, finds extensive applications in optical information processing and adaptive optics, thus making it an indispensable tool in these fields. Using cascaded spatial light modulators can efficiently and superbly generate a higher-order Hermite–Gaussian mode; however, the experimental system is challenging, and there are many influencing factors, such as the misalignment between the optical field on the plane of the second spatial light modulator and the hologram loaded onto it, as well as the spot size of the optical field on the plane of the second spatial light modulator. In this paper, we analyzed the influence of the above factors on the quality of generating a higher-order Hermite–Gaussian mode, providing a reference for the efficient and high-quality generation of the higher-order Hermite–Gaussian mode.

Nonlinear photonic crystals made from polystyrene materials that have Kerr nonlinearity can exhibit ultrafast optical switching when the samples are pumped by ultrashort optical pulses with high intensity due to the change of the refractive index of polystyrene and subsequent shift of the band gap edge or defect state resonant frequency. Polystyrene has a large Kerr nonlinear susceptibility and almost instantaneous response to pump light, making it suitable for the realization of ultrafast optical switching with a response time as short as a few femtoseconds. In this paper, we review our experimental progress on the continual improvement of all-optical switching speed in two-dimensional and three-dimensional polystyrene nonlinear photonic crystals in the past years. Several relevant issues are discussed and analyzed, including different mechanisms for all-optical switching, preparation of nonlinear photonic crystal samples by means of microfabrication and self-assembly techniques, characterization of optical switching performance by means of femtosecond pump-probe technique, and different ways to lower the pump power of optical switching to facilitate practical applications in optical information processing. Finally, a brief summary and a perspective of future work are provided.

Quantum well lasers have attracted a great deal of attention by their many advantages such as low threshold current density, excellent temperature feature, high modulation rate and wavelength adjustability etc. The investigation on quantum well laser in mainland China started in the early 80s. AlGaAs/GaAs QW laser diode and InGaAs/GaAs strained layer QW laser diode have been developed using MBE technology with extremely low threshold current and high T0. Now the growth technologies for QW structure have been expanded to MOCVD technology. Emission wavelengths, on longer wavelength sides have been expanded up to 1.3 µm and 1.55 µm with InGaAsP/InP material system for application in optical fiber communication. On shorter wavelength sides, the emission wavelength has been expanded to lower than 670 nm, for applications in optical information processing. The characteristics of these devices will be demonstrated in this paper. The QW-DFB LD and low-dimension quantum wire and quantum dot lasers are under investigation.

We propose a scheme to realize slow-light soliton beam splitters by using a tripod-type four-level atomic system. We show that optical solitons, which have ultraslow propagation velocity and ultralow generation power, can be generated in the system via electromagnetically induced transparency and can be stored and retrieved with high efficiency and fidelity. In particular, a nonlinear beam splitter that splits one optical soliton into two or more ones can be obtained by switching on and off of two or more control laser fields subsequently. The results reported here open a route not only for active manipulation of nonlinear optical pulses in multistate quantum systems but also for promising applications in optical information processing and transmission.

$X$ waves are a special type of wave packet that can maintain their transverse profile of $X$ shape during propagation, and they are of much interest for the study of fundamental physics and practical applications. Here we present a scheme to generate nonlinear $X$ waves and realize their active control by using a cold gas of Rydberg atoms via electromagnetically induced transparency (EIT). We show that, due to the EIT effect contributed by a control laser field and the strong, nonlocal Kerr nonlinearity contributed by Rydberg-Rydberg interaction between atoms, the system supports high-dimensional, nonlocal, and nonlinear optical $X$ waves, which have low propagation loss, ultraslow propagation velocity, and ultralow generation power. We also show that the stability domain of such $X$ waves can be greatly enlarged by increasing the nonlocality degree of the Kerr nonlinearity, and their motion trajectory can be manipulated by using an external magnetic field. Our study opens a route for generating and controlling nonlocal ultraslow nonlinear optical $X$ waves, which may have promising applications in optical information processing and transmission.

Image-amplifying optical cavities offer an intriguing platform for nonlinear optical processing of two-dimensional signals, with potential applications in optical information processing and optically implemented artificial neural networks. Here, we analyze the performance of a self-imaging degenerate cavity via numerical simulations and show the existence of a cavity size-dependent minimum spread in the transverse mode resonances. This non-degeneracy, in turn, leads to an inherent trade-off between the amplification and the fidelity of the intracavity image as the cavity finesse changes. Our results point to a promising path to nonlinear image processing in a low-power, small-form-factor optical cavity.

Chiral organic materials have garnered significant interest in nanophononics due to their ability to manipulate polarized light and encode optical information. Herein, chiral one‐dimensional (1D) organic microplates based on benzocyclazine form homochiral crystals that exhibit excellent optical waveguiding properties. These microplates exhibited highly asymmetric light propagation that depends on the handedness of circularly polarized light (CPL). These homochiral microplates demonstrated selective transmission, with R‐microplate favouring left‐handed CPL and S‐microplate favouring right‐handed CPL, showcasing distinct optical loss coefficients for each enantiomer. Multichannel light propagation was observed, where the intensity varied based on the excitation position. These results highlight the potential of 1D chiral microplates for advanced nanophotonic devices, offering chiral‐dependent control over light transmission for future applications in optical information processing.

We study electromagnetically induced transparency (EIT) and nonlinear pulse propagation in a resonant atomic gas confined in a microwaveguide. We find that the quantum-interference effect in this system can be greatly enhanced due to the reduction of the mode volume of the optical field. In particular, compared with atomic gases in free space, the EIT transparency window in the present confined system can be much wider and deeper, the group velocity of the probe field can be much slower, and the Kerr nonlinearity of the system can be much stronger. We show that a more efficient production of ultraslow optical solitons in the present system may be achieved with much slower propagating velocity and lower generation power. Features of EIT and pulse propagation in the present system are very promising for practical applications in optical information processing and transmission.

The paper represents a brief overview on theoretical and experimental investigations of feedback acousto-optic systems carried out in Moscow State University in recent years. These systems are of great interest by reason of their complicated and intriguing behavior as well as in view of novel applications in optical information processing.

Optical chirality, which plays important roles in liquid crystal display and biological and chemical detection, has been attracting scientists' attention due to its potential applications in optical information processing. Usually, the chiral optical response of natural molecules is very weak. However, the emergence of metasurfaces offers a promising solution to solve this issue. By judiciously designing the geometry of meta-atoms, we have realized strong optical circular dichroism (CD) in both linear and nonlinear optical regimes. However, tuning of the CD with a metasurface remains challenging. Here, we propose the twist-angle-controlled nonlinear CD effect by using the second-harmonic generation process on a gold-crystal hybrid metasurface. The CD effect of the second-harmonic waves can be tuned well by controlling the twist angle between the two constituent materials. The proposed hybrid metasurface may open new avenues for developing ultracompact and multifunctional nonlinear optical devices.

Photorefractive crystals of the sillenites (Bi12GeO20, Bi12SiO20, Bi12TiO20) have the promising applications in optical information processing, including spatial light modulators, optical memories, phase conjugation, image inversion, and optical interconnects.1 In comparison to other sillenities, bismuth titanium oxide (Bi12TiO20, BTO) exhibits a higher sensitivity for red lights that permit the use of a cheap HeNe laser. In addition, BTO crystals have a lower optical activity ρ, which is favourable for many applications. However, some technological problems (the incongruent melting of Bi12TiO20, the high tendency of Bi2O3-containing melts to the supercooling, etc.) created difficulties for producing large single crystals of high optical quality.

When studying the spin-noise-induced fluctuations of Kerr rotation in a quantum-well microcavity, we have found a dramatic increase of the noise signal (by more than two orders of magnitude) in the vicinity of anti-crossing of the polariton branches. The effect is explained by nonlinear optical instability of the microcavity giving rise to the light-power-controlled amplification of the polarization noise signal. In the framework of the developed model of built-in amplifier, we also interpret the nontrivial spectral and intensity-related properties of the observed noise signal below the region of anti-crossing of polariton branches. The discovered effect of optically controllable amplification of broadband polarization signals in microcavities in the regime of optical instability may be of interest for detecting weak oscillations of optical anisotropy in fundamental research and for other applications in optical information processing.